A novel approach for determining fatigue resistances of different muscle groups in static cases

In ergonomics and biomechanics, muscle fatigue models based on maximum endurance time (MET) models are often used to integrate fatigue effect into ergonomic and biomechanical application. However, due to the empirical principle of those MET models, the disadvantages of this method are: 1) the MET models cannot reveal the muscle physiology background very well; 2) there is no general formation for those MET models to predict MET. In this paper, a theoretical MET model is extended from a simple muscle fatigue model with consideration of the external load and maximum voluntary contraction in passive static exertion cases. The universal availability of the extended MET model is analyzed in comparison to 24 existing empirical MET models. Using mathematical regression method, 21 of the 24 MET models have intraclass correlations over 0.9, which means the extended MET model could replace the existing MET models in a general and computationally efficient way. In addition, an important parameter, fatigability (or fatigue resistance) of different muscle groups, could be calculated via the mathematical regression approach. Its mean value and its standard deviation are useful for predicting MET values of a given population during static operations. The possible reasons influencing the fatigue resistance were classified and discussed, and it is still a very challenging work to find out the quantitative relationship between the fatigue resistance and the influencing factors

Muscle Fatigue Analysis Using OpenSim

In this research, attempts are made to conduct concrete muscle fatigue analysis of arbitrary motions on OpenSim, a digital human modeling platform. A plug-in is written on the base of a muscle fatigue model, which makes it possible to calculate the decline of force-output capability of each muscle along time. The plug-in is tested on a three-dimensional, 29 degree-of-freedom human model. Motion data is obtained by motion capturing during an arbitrary running at a speed of 3.96 m/s. Ten muscles are selected for concrete analysis. As a result, the force-output capability of these muscles reduced to 60%-70% after 10 minutes' running, on a general basis. Erector spinae, which loses 39.2% of its maximal capability, is found to be more fatigue-exposed than the others. The influence of subject attributes (fatigability) is evaluated and discussed

The dynamic and static strength of whole body exertions in the human

The characteristics of whole body manual exertions were investigated in both males and females under a wide range of conditions of posture, hand height, direction of exertion and task resistance. Many of these conditions were novel. The many factors which influence force exertion were reviewed and a computerized bibliography on human strength was prepared. Two experimental studies investigated the influence and interrelationships of hand/handle interface, gravitational and musculo-skeletal limitations on the ability to produce maximal static forces. A third study introduced novel strength testing equipment, protocol, data processing and display techniques in order to extend the measurement and analysis into three dimensions. A final study compared static lifting strength with maximal one and two-handed dynamic lifting performance against a range of resistances on an isoresistive hydrodynamometer. A good association was found between dynamic and static measures of whole body strength. However, different relationships between the two were observed in one and two-handed, and in male and female exertions. It was further concluded that dynamic and static measures of whole body strength cannot reliably be predicted on the basis of body weight and stature alone when the exerted force is directed along the line joining the foot and hand centroids. In other directions of exertion, where gravitational limitations play a more dominant role in the strength of exertion, reasonable predictions of whole body static strength may be obtained using a simple linear regression model with body weight and stature as independent variables. Extension of the Postural Stability Diagram into three dimensions and dynamic models of lifting strength based on the results are discussed as possible aids for task analysis in manual materials handling

A Full-chain OpenSim Model and Its Application on Posture Analysis of an Overhead Drilling Task

International audienceBiomechanical motion simulation and kinectic analysis of human joints and muscles provide insights into Musculoskeletal disorders. OpenSim is an open-source platform that give easy access to biome-chanical analysis, especially of muscles. The biomechanical analysis in OpenSim is based on pre-defined human models. Among the dozens of models available right now, none covers the muscles and joints of all the body parts. In view of the fact that most human motions are systemic, the lack of a comprehensive model prohibits synthesized and systemat-ical biomechanical analysis. The aim of this research is to develop an OpenSim model which enables the full-chain dynamic analysis of tasks involving multi-bodies. The model is developed based on two existing models. It consists of 45 body segments, 424 muscles and 39 degrees of freedom. The model was then used to simulate an overhead drilling task. Six drilling postures are analyzed, and the estimated joint moments and muscle activations are compared

Control design of a de-weighting upper-limb exoskeleton: extended-based fuzzy

One of the most common issues to human is fatigue. A technology known as exoskeleton has been identified as one of the solutions to address this issue. However, there are two issues that need to be solved. One of them is the control approach. Hence, the main aim of this work, is to investigate the control design for upper-limb exoskeleton. An extended based fuzzy control is proposed to observe the effectiveness of the exoskeleton in dealing with human with different strength. Three conditions of human strength were applied. PID was used for a comparison purpose. It is shown that with the proposed control approach, the exoskeleton can assist human to achieve the desired trajectory accurately with a minimal amount of torque required

Training for muscular power adaptations : the role of contraction type and velocity

Muscular power, an integral component in most sport, is the product of force and velocity. Power is often viewed as synonymous, yet incorrectly, with strength. Where power has an inherent speed component, strength is independent of movement velocity, and is a measure of a muscle’s ability to produce a maximal force. In a majority of athletic events power is requisite to success, and is often more decisive in performance outcomes than strength alone. Currently, results from existing research examining the effectiveness of differing velocities of contraction in improving maximal power are mixed. Common methodologies used in research settings to study muscular power changes are isotonic training, isokinetic training, isometric training, and plyometric training. However, little research has been done examining the potential efficacy of training using inertial loading. This report examines existing research on movement velocities and loads, compares the effects of training velocities for increasing maximal power, identifies shortfalls and information gaps, and recommends future research in training for muscular power adaptations and improved athletic performance. This report also provides a detailed description of inertial load training and establishes a theoretical study design, hypothesis, and reasoning outlining why and how inertial load training may elicit muscular power increases and improved athletic performance.Kinesiology and Health Educatio

A biomechanical investigation of contemporary powerlifting training practices and their potential application to athletic development.

The contemporary training practices of powerlifters are presently being adopted by athletes from a variety of sports, seeking to improve their performance. The aims of this PhD were to: 1) identify the contemporary training practices of powerlifters; 2) investigate the biomechanical stimulus the training practices create; and 3) assess whether the training practices have the potential to improve the athletic performance of general athletes. The aims were achieved through the completion of five related studies. The first study employed questionnaires and interviews to identify the contemporary training practices used by elite powerlifters. The results demonstrated that elite powerlifters used a wide variety of training practices, many of which would not have been attributed to the group based on previous literature. The practices were categorised based on their underlying mechanical principles, so that the essential features could be investigated in the subsequent studies. A regression-based approach was used in the second study to identify the biomechanical variables associated with performance of common sporting tasks. Maximum force production, power, velocity and rate of force development (RFD) were shown to explain a large percentage of variation in performance of tasks such as sprinting, jumping and changing direction (adjusted R2 ranged from 0.43 to 0.86). These mechanical variables were then measured in a series of experimental studies to assess the potential of the contemporary powerlifting practices to improve athletes' physical performance. Assessments were based on a central paradigm in strength and conditioning, which asserts that improvements in the ability to express biomechanical variables (e.g. force and power) are best obtained with training practices that maximise acute production of the same variable. Based on the categorisation of the mechanical principles underlying the assessed training practices, three experimental studies were conducted that investigated: 1) the practice of performing traditional resistance exercises at maximum velocity; 2) the effects of manipulating the external resistance through the use of variable resistance material (chain resistance) and an unconventional barbell (the hexagonal barbell); and 3) the effects of altering the movement strategy used to perform the squat. The results of the studies clearly demonstrated that each of the practices investigated could be used to substantially alter - and, in most cases, enhance - the biomechanical stimulus created. The practice of performing traditional resistance exercises at maximum velocity revealed that all key mechanical variables were significantly increased (p < 0.05) compared with the standard practice of performing repetitions with a sub-maximum velocity. The results additionally demonstrated that, when performing a traditional resistance exercise such as the deadlift at maximum velocity, experienced resistance trained athletes could accelerate the load for the majority (75% to 90%+) of the movement. The second experimental study featuring the separate use of chain resistance and the hexagonal barbell to alter the characteristics of the external resistance demonstrated contrasting effects. The change in position of the external resistance when using the hexagonal barbell significantly (p < 0.05) increased the participants' ability to produce high force, power, velocity and RFD values across a range of loads in comparison with the same movement performed with a traditional straight barbell. In contrast, the results from the study evaluating the effects of adding chain resistance showed that, whilst force values were increased with the addition of chains, velocity, power and RFD values substantially decreased compared to standard repetitions performed with only barbell resistance. The results also demonstrated that the effects of the chain resistance were more noticeable with heavier chain and barbell loads. The final experiment investigated the effects of altering the movement strategy used to perform the back squat exercise. The results confirmed that changes to the movement strategy had a significant effect on a range of kinematic and kinetic variables. In particular, the contemporary techniques promoted by powerlifters resulted in substantial kinematic and kinetic changes at the hip and reduced kinetic output at the ankle joint. Collectively, the work from this PhD supports the selective use of contemporary powerlifting training practices for the development of athletic potential. Future research should build on the framework created in this thesis, progressing to longitudinal and ultimately implementation studies to increase the likelihood of transferring the results to practice

Model-free Optimization of Trajectory And Impedance Parameters on Exercise Robots With Applications To Human Performance And Rehabilitation

This dissertation focuses on the study and optimization of human training and its physiological effects through the use of advanced exercise machines (AEMs). These machines provide an invaluable contribution to advanced training by combining exercise physiology with technology. Unlike conventional exercise machines (CEMs), AEMs provide controllable trajectories and impedances by using electric motors and control systems. Therefore, they can produce various patterns even in the absence of gravity. Moreover, the ability of the AEMs to target multiple physiological systems makes them the best available option to improve human performance and rehabilitation. During the early stage of the research, the physiological effects produced under training by the manual regulation of the trajectory and impedance parameters of the AEMs were studied. Human dynamics appear as not only complex but also unique and time-varying due to the particular features of each person such as its musculoskeletal distribution, level of fatigue,fitness condition, hydration, etc. However, the possibility of the optimization of the AEM training parameters by using physiological effects was likely, thus the optimization objective started to be formulated. Some previous research suggests that a model-based optimization of advanced training is complicated for real-time environments as a consequence of the high level of v complexity, computational cost, and especially the many unidentifiable parameters. Moreover, a model-based method differs from person to person and it would require periodic updates based on physical and psychological variations in the user. Consequently, we aimed to develop a model-free optimization framework based on the use of Extremum Seeking Control (ESC). ESC is a non-model based controller for real-time optimization which its main advantage over similar controllers is its ability to deal with unknown plants. This framework uses a physiological effect of training as bio-feedback. Three different frameworks were performed for single-variable and multi-variable optimization of trajectory and impedance parameters. Based on the framework, the objective is achieved by seeking the optimal trajectory and/or impedance parameters associated with the orientation of the ellipsoidal path to be tracked by the user and the stiffness property of the resistance by using weighted measures of muscle activations

Tactile myography: an off-line assessment on intact subjects and one upper-limb disabled

Castellini C, Kõiva R, Pasluosta C, Viegas C, Eskofier BM. Tactile myography: an off-line assessment on intact subjects and one upper-limb disabled. Technologies / SI: Assistive Robotics. 2018;6(2): 38.Human-machine interfaces to control prosthetic devices still suffer from scarce dexterity and low reliability; for this reason, the community of assistive robotics is exploring novel solutions to the problem of myocontrol. In this work, we present experimental results pointing in the direction that one such method, namely Tactile Myography (TMG), can improve the situation. In particular, we use a shape-conformable high-resolution tactile bracelet wrapped around the forearm/residual limb to discriminate several wrist and finger activations performed by able-bodied subjects and a trans-radial amputee. Several combinations of features/classifiers were tested to discriminate among the activations. The balanced accuracy obtained by the best classifier/feature combination was on average 89.15% (able-bodied subjects) and 88.72% (amputated subject); when considering wrist activations only, the results were on average 98.44% for the able-bodied subjects and 98.72% for the amputee. The results obtained from the amputee were comparable to those obtained by the able-bodied subjects. This suggests that TMG is a viable technique for myoprosthetic control, either as a replacement of or as a companion to traditional surface electromyography